The present invention relates to a piston suspension for a reciprocating piston engine and to an engine incorporating the suspension.
The tilt play of a piston in a reciprocating piston engine, for example in a four-stroke reciprocating piston engine, has been known and researched for a long time. In this connection see, for example, Carl Riedel "Konstruktion und Berechnung moderner Automobile- und Kraftradmotoren", 2nd Edition, Berlin 1931, page 141, FIG. 144.
In order to balance out the forces which arise at the reciprocating piston due to the tilt play, constructional measures are necessary apart from the use of lubricant. In the case of a four-stroke reciprocating piston engine the piston moves not only upwardly and downwardly, but also laterally in the connecting rod plane. During this motion, the piston changes cylinder side, against which it presses, six times per working cycle, i.e. in two revolutions. The thus arising friction causes about 50 to 75% of the mechanical friction loss. In order to alleviate the resulting forces and the effect thereof on material, laterally offset shafts, among other things, are used in engine construction. The crankshaft does not lie exactly centrally under the piston, but is slightly laterally displaced.
Equally, it is usual to offset the piston gudgeon pins (DE-OS 2 751 932) so that the impacts when cylinder side exchange occurs are softer and the piston has a rolling action relative to the cylinder wall. By this means, the lateral forces of the piston can be alleviated. However, the remaining lateral forces must be picked up by a lubricant film to prevent the piston from scuffing the cylinder wall.
A further known measure which alleviates the lateral forces of the piston is a piston suspension by means of a crosshead, as employed in, in particular, double-acting steam engines.
Also known are constructions in which the pistons are suspended at guided rods which run in linear bearings and terminate at one end in a crosshead. These have been used for, in particular, locomotives.
In the aforementioned constructions a lubricant is present in the working chamber for the piston or in the spaces adjoining the working chamber.
All the above-described constructions in practice function only with lubricant.
A construction which has become known under the name Philips rhombic gear by R. J. MEIJER (DE-AS 1 080 351) hardly needs a lubricant in the working chamber for the piston. In order to alleviate the substantially higher friction of the rhombic gear caused by the gearwheels, the gearwheels are lubricated or greased. For the case where use requires a lubricant-free working chamber, the piston has to seal off the crankcase relative to the working chamber.
The same is also true for the connecting rod arrangement according to FICHT with crank guide (DE-OS 3 433 510). Due to the transmission by means of a connecting rod movable in only one point, the Philips rhombic gear piston suspension and the piston suspension of Ficht have only small tilt play of the piston,
Excepting the piston mounting by means of linearly guided piston rods at both piston sides, all known piston suspensions have a tilt play of the piston, caused by the movable connecting means connected at one rotational point. The piston has play relative to the cylinder wall and is able to move on the cylinder wall. This movement is mostly a rotary movement which emanates from the rotational mounting of the force-receiving component at the piston suspension. In the example with the rhombic gear, the tilt play is restricted to play in the toothing of the gearwheels, this play being multiplied by the lever effect from the point of engagement of the gearwheels up to the wedge point at the piston.
In the example with piston rods at both sides of the piston this play is restricted to the bearing play of the piston rods. However, this piston rod bearing is difficult to properly seal off from the working chamber and exhibits high friction losses.
In the case of all the aforedescribed constructions a lubrication of the piston or the piston rods is required in order to avoid scuffing.
A dry slide bearing instead of a lubricant, for example, a polyimide bearing of the kind available under the name "Vespel" from Dupont in France, has not proved itself in practice. The tilt play leads to higher wear rates, so that sealing leakages arise after a certain time.
Up to now there is thus no long-life reciprocating piston engine, operating as a motor, which can manage without lubricant In the case of dry running reciprocating piston pumps the problems are similar, the substantially lower pressures being less conducive to wear than the pressure peaks in motors.